A 13-year-old boy presented with symptoms and signs of a posterior 3rd ventricle tumor associated with raised levels of serum and cerebrospinal alpha-fetoprotein. The patient underwent subtotal resection of the tumor followed by craniospinal radiation. Histopathological examination revealed a pure endodermal sinus tumor. Endodermal sinus tumors represent a rare type of germ cell tumor, only 13 intracranial cases having been reported in the literature.